Prior door operating systems use an apparatus which attaches to the door and door knob. Examples of this type of door operating system are found in U.S. Pat. Nos. 5,050,346 and 5,095,654. Generally, these known operating systems use an air compressor, actuated by a transmitter/receiver, for charging fluid lines in the door operating system. The known device includes a first sub-assembly comprising an air cylinder, mounted on the door frame and door, which provides an opening force. A second sub-assembly also comprising an air cylinder provides force to a rack-and-pinion type mechanism for turning the door's dead-bolt and door knob. The second sub-assembly further includes a strap which is mounted to a push rod at one end of the air cylinder with another end of the strap wrapped around the door knob for rotation of the same. The rack-and-pinion portion of the second sub-assembly requires a clam shell type structure fastened to the dead bolt by a clamp having teeth for meshing with the rack. The air cylinder of the second sub-assembly includes springs for retraction of the push rod and rack. After de-activation of the air compressor by remote control, the door is closed by a force which is provided by a torsion spring mounted in the first sub-assembly.
An advantage of the known door operating system is that it provides a way of opening a door from a remote location. A further advantage of the system is that it can be retro-fitted to an existing door. Some disadvantages of the known door operating system include the number of specialized parts required (which increases cost), and the cost of the labor used to assemble the parts. Moreover, as moving parts are exposed, there is a risk of injury regarding the operation of the second sub-assembly, e.g. where a child or animal could get a body part pinched or entangled in the sub-assembly as it is being activated or deactivated. Further, because it is exposed to casual observation in a home or office living environment it may not present an aesthetically pleasing door hanging, for example, because of the industrial-looking nature of the parts. Furthermore, the known device interferes with the normal operation of the door knob and dead bolt; moreover, the known device includes a compressor which must continuously run to hold the door open which is a disadvantage because it contributes to the noise and energy inefficiency of the system.
Other known door operating systems use an electromagnetic motor to drive an opening mechanism; however, these systems generate noise when in operation, do not provide for unlatching of a door latch, and are costly to purchase and install.
It is therefore desired from the standpoint of cost, ease of assembly and operation, safety, and number of parts, a door operating system which opens gently, is easy to install and to relocate, of low cost and is easy to maintain, but is compact, reliable, and is basically safe in operation.